A PWM motor drive using synchronous rectification is disclosed in Japanese Patent Laid-Open No. 5-211780 and so on.
FIG. 15 shows a conventional single-phase motor drive.
Reference numeral 1 denotes a power switch circuit, reference numeral 2 denotes a synthesizing circuit, reference numeral 3 denotes a PWM signal generation circuit, and reference numeral 4 denotes a single-phase motor coil. An output circuit for driving the single-phase motor coil 4 by PWM chopping makes a bridge connection of switching elements 5, 6, 7, and 8. The ends of the switching elements 5, 6, 7, and 8 that make a bridge connection are connected to a pole 10 of a power supply and the other ends of the switching elements are grounded to the other pole of the power supply via a current detection resistor 15 serving as a current detector. The single-phase motor coil 4 is connected on a midpoint of the switching elements 5, 6, 7, and 8 that make a bridge connection. In the following explanation, the switching elements 5 and 7 will be referred to as upper arm transistors and the switching elements 6 and 8 will be referred to as lower arm transistors.
The following will discuss operations of the single-phase motor drive shown in FIG. 15.
First an energization phase is determined by the power switch circuit 1. When the upper arm transistors 5 and the lower arm transistors 8 are conducting, current applied to the coil 4 flows to the current detection resistor 15. When the current reaches the coil current corresponding to a torque command voltage S14, the current is detected by a current detection circuit 11. The current detection circuit 11 changes its output and the output is inputted to the PWM signal generation circuit 3.
The output signal of the PWM signal generation circuit 3 is synthesized with the output signal of the power switch circuit 1 in the synthesizing circuit 2. When a transistor on the PWM driving side is driven by the lower arm, the lower arm transistor 8 is nonconducting and the upper arm transistor 7 is conducting. At this point, a current I4 applied to the coil 4 keeps flowing to the upper arm transistors 5 and 7 but gradually decreases. At a given moment, the upper arm transistor 7 is made nonconducting and the lower arm transistor 8 is made conducting again by the output of the PWM signal generation circuit 3 and a coil current is increased. PWM operation is performed by repeating these operations.
FIG. 16 is a timing chart of output signals and a motor current driven by the single-phase motor drive shown in FIG. 15. FIG. 16 shows output signals S1 to S4 of the power switch circuit 1, signals S6 to S9 which are the output signals of the synthesizing circuit 2 and the gate input signals of the upper arm transistors and the lower arm transistors, a voltage S12 generated in the current detection resistor 15, the torque command voltage S14, an output signal S15 of the current detection circuit 11, an output S5 of the PWM signal generation circuit 3, and the current I4 applied to the motor coil 4. In FIG. 15, the outputs S1 to S4 of the power switch circuit 1 output the signals S6 to S9 for bringing the upper arm transistor 5 and the lower arm transistor 8 into conduction and the signals S6 to S9 are inputted to the synthesizing circuit 2. In this state, S5 is outputted from the PWM signal generation circuit 3 at given moment t1 and is inputted to the synthesizing circuit 2, the signals S6 to S9 are outputted from the synthesizing circuit 2, the upper arm transistor 5 and the lower arm transistor 8 are made conducting, the coil current I4 gradually increases, and the voltage S12 generated in the current detection resistor 15 also increases. When the voltage S12 generated in the current detection resistor 15 reaches at moment t2 the voltage S14 determined by a torque command signal, the output S15 of the current detection circuit 11 is changed and is inputted to the PWM signal generation circuit 3, the output signal S5 of the PWM signal generation circuit 3 is inputted to the synthesizing circuit 2 to have a regenerative state, and the synthesizing circuit 2 outputs S6 to S9, so that the lower arm transistor 8 is made nonconducting and the upper arm transistor 7 is made conducting.
At moments t2 and t3, the upper arm transistors 5 and 7 are conducting and the current I4 of the coil 4 becomes a regenerative current and gradually decreases. At moment t3, S5 is outputted again from the PWM signal generation circuit with arbitrary timing and the signals S6 to S9 are outputted from the synthesizing circuit 2, the upper arm transistor 5 and the lower arm transistor 8 are made conducting, the coil current I4 gradually increases, and the voltage S12 generated in the current detection resistor 15 also increases. By repeating this operation, it is possible to apply the current I4 almost equivalent to the torque command voltage S14 to the motor coil 4.
FIG. 17 shows a conventional three-phase motor drive. Reference numeral C1 denotes a power switch circuit, reference numeral C2 denotes a synthesizing circuit, reference numeral C3 denotes a PWM signal generation circuit, reference numeral C4 denotes a three-phase motor coil, reference numerals C5, C7, and C17 denote upper arm transistors, reference numerals C6, C8, and C18 denote lower arm transistors, reference numeral 10 denotes a power supply, reference numeral C11 denotes a current detection circuit, and reference numeral C15 denotes a current detection resistor.
The following will discuss operations of the three-phase motor drive shown in FIG. 17.
First an energization phase is determined by the power switch circuit C1. When the upper arm transistors C5 and the lower arm transistors C8 are conducting and the upper arm transistors C7 and C17 and the lower arm transistors C6 and C18 are nonconducting, current applied to the motor coil C4 flows to the current detection resistor C15. When the current reaches a coil current corresponding to a torque command voltage SC14, the current is detected by the current detection circuit C11. The current detection circuit C11 changes its output and the output is inputted to the PWM signal generation circuit C3. The output signal of the PWM signal generation circuit C3 is synthesized with the output signal of the power switch circuit C1 in the synthesizing circuit C2. When a transistor on the PWM driving side is driven by the lower arm, the lower arm transistor C8 is nonconducting and the upper arm transistor C7 is conducting. At this point, currents IC4 and IC5 applied to the motor coil C4 keep flowing to the upper arm transistors C5 and C7 but gradually decrease. At a given moment, the upper arm transistor C7 is made nonconducting and the lower arm transistor C8 is made conducting again by the output of the PWM signal generation circuit C3 and a coil current is increased. PWM operation is performed by repeating these operations.
FIGS. 18 and 19 are time charts of output signals and a motor current driven by the three-phase motor drive of FIG. 17. FIG. 18 is an overall view and FIG. 19 is an enlarged view of period T1 shown in FIG. 18. FIGS. 18 and 19 show output signals SC1 to SC4, SC17, and SC18 of the power switch circuit C1, signals SC6 to SC9, SC19, and SC20 which are the output signals of the synthesizing circuit C2 and the gate input signals of the upper arm transistors and the lower arm transistors, a voltage SC12 generated in the current detection resistor C15, a torque command voltage SC14, an output signal SC15 of the current detection circuit C11, an output signal SC5 of the PWM signal generation circuit C3, and currents IC4 to IC6 applied to the motor coil C4. In FIG. 17, the outputs SC1 to SC4, SC17, and SC18 of the power switch circuit C1 output the signals SC6 to SC9, SC19, and SC20 for bringing the upper arm transistor C5 and the lower arm transistor C8 into conduction and the signals are inputted to the synthesizing circuit C2. In this state, SC5 is outputted from the PWM signal generation circuit C3 at given moment tc1 and is inputted to the synthesizing circuit C2, the signals SC6 to SC9, SC19, and SC20 are outputted from the synthesizing circuit C2, the upper arm transistor C5 and the lower arm transistor C8 are made conducting, the coil currents IC4 and IC5 gradually increase, and the voltage SC12 generated in the current detection resistor C15 also increases. When the voltage SC12 generated in the current detection resistor C15 reaches at moment tc2 the voltage SC14 determined by a torque command signal, the output SC15 of the current detection circuit C11 is changed and is inputted to the PWM signal generation circuit C3, the output signal SC5 of the PWM signal generation circuit C3 is inputted to the synthesizing circuit C2 to have a regenerative state, and the synthesizing circuit C2 outputs SC6 to SC9, SC19, and SC20, so that the lower arm transistor C8 is made nonconducting and the upper arm transistor C7 is made conducting.
At moments tc2 and tc3, the upper arm transistors C5 and C7 are conducting and the currents IC4 and IC5 of the motor coil C4 become regenerative currents and gradually decrease. At moment tc3, SC5 is outputted again from the PWM signal generation circuit with arbitrary timing and the signals SC6 to SC9, SC19, and SC20 are outputted from the synthesizing circuit C2, the upper arm transistor C5 and the lower arm transistor C8 are made conducting, the coil currents IC4 and IC5 gradually increase, and the voltage SC12 generated in the current detection resistor C15 also increases. By repeating this operation, it is possible to apply the current IC4 almost equivalent to the torque command voltage SC14 to the motor coil C4. In FIG. 18, the operation of FIG. 19 is performed in an energized state determined by the outputs of SC1 to SC4, SC17, and SC18 of the power switch circuit.
However, the conventional configuration regenerates the motor coil current while the two transistors are made conducting, resulting in large power consumption.
Further, the conventional configuration requires a current detection resistor for detecting a large motor coil current. Due to large power consumption, it is difficult to integrate the current detection resistor into an integrated circuit, resulting in a large apparatus with a high cost.
The present invention is devised to solve the conventional problem and has as its object the provision of a motor drive which can integrate a current detection resistor into an integrated circuit and can reduce power consumption during regeneration.